The management of diseases based on inborn errors of metabolism could be significantly improved if simple, low cost means for the measurement of the biochemical abnormality were readily available to patients in the home environment. Although all states and most developed nations have effective screening programs for newborns, the management of patients diagnosed with PKU and related diseases can be significantly improved. We propose to apply a unique NADH based bioluminescence based detection system in a simple, direct reading format to the determination of phenylalanine in plasma and urine. We avoid the problem of the need for instrumentation to measure the intensity of the light output, by application of a proprietary technology where the spatial position of the light is directly related to the concentration of the substrate of interest. The spatial approach has greatly simplified the detection problem and even permits direct visual detection. We propose to demonstrate the feasibility of this approach to phenylalanine measurement for the diagnosis of hyperphenylalanemia and for the management of diseases related to disorders in phenylalanine metabolism. PROPOSED COMMERCIAL APPLICATION Applications include hospitals, birthing clinics, state public health labs, and HMO/PPO clinics and labs. Parents will be able to monitor phenylalanine concentrations for safe disease management. Very inexpensive sensing will expand PKU screening to third world applications.